EXPOSURE AND GROWTH AND DEVELOPMENT 241 



processes, uptake and loss. Leaf saturation deficits can be produced by an 

 adverse soil moisture regime. Experiments were therefore carried out in 

 which plants of Helianthus annuus were grown at a range of soil moisture 

 conditions from field capacity to one sixteenth field capacity (Whitehead, 



• ISO 



• LOSS IN mg/cm^/hour 

 O LOSS per PLANT 

 O LEAP AREA 



E 



T 

 10 



20 

 Wind speed ( m.p.h.) 



Fig. 5. Water loss of plants o{ Helianthus annuus in 6 hours. These four sets of plants 

 were grown for 30 days at i niile/h, 9 mile/h, 19 mile/h and 33 mile/h respectively. 

 After bringing their substrate up to field capacity they were exposed to a 33 mile/h 

 wind for 6 hours. The total loss per plant is shown in relation to leaf area per plant 

 and its loss per unit area in unit time. 



1962). The results of these experiments are shown in Fig. 6. It can be seen 

 that anatomical and morphological changes essentially similar to those 

 produced by exposure to wind resulted from these treatments. Again the 

 main effect appeared to have been on the processes of differentiation 

 except that at the most adverse regime some interference with the actual 

 photosynthetic apparatus appears to have occurred. 



The other factor associated with wind effect, i.e. precipitation, would be 

 expected to offset the effect of wind in lowering the water balance of the 



